1. Field of the Invention
The present invention relates to a shaped groove countermatrix for a rotary groove pulley matrix and countermatrix bending head pipe bending machines.
2. Description of the Related Art
The operating principle of such machines is to stress a pipe to be bent to bending, thus arranging the latter between the grooves of the matrix and of the countermatrix and making the pulley matrix to rotate on its axis, which pulley matrix is assembled on a driving shaft and drags the pipe along a bending path by friction in its groove.
In order to reduce ovalization as much as possible and to avoid wrinkling and breaking of the pipe during the bending operation, countermatrices are used in the prior art and have grooves shaped according to suitable geometries, as is exemplified in Italian Patent Nos. 1.147.601 and 1.172.068, granted to the same Applicants for a U.S. Patent on the present invention.
Moreover, in most cases one proceeds to the lubrication of the contact between the pipe and the countermatrix, to avoid seizures during the bending operation. This lubrication must, for instance, be carried out necessarily for aluminum pipes and for pipes with a sheath in plastic. The lubricant is sprayed or applied with a brush.
The shaped groove of the prior art that better achieves its end has been suggested by the same applicants for a U.S. Patent on the present invention, and has a semicircular cross section except in an end tract, which is the exit in the sense of a feed of the pipe during the bending operation. Such an end tract is tapered both longitudinally and transversely towards the exit edge, starting from a semicircular cross section of the groove itself, and has its cross section made up of two ellipses with their major axes parallel to and slightly offset from the plane of longitudinal symmetry of the groove, which ellipses are equal to each other and inferiorly radiused by a tract which is elliptic too.
However, such a countermatrix has the problem that the pipes bent utilizing it show a visible circular tapering at the ends of the bending tracts.
As regards the lubrication of the preceding countermatrices to prepare them for the bending operation, such lubrication has the shortcoming of being difficult and time consuming.